Structure and method of integrated circuit having decouple capacitance

ABSTRACT

The present disclosure provides an integrated circuit that includes a circuit formed on a semiconductor substrate; and a de-cap device formed on the semiconductor substrate and integrated with the circuit. The de-cap device includes a filed-effect transistor (FET) that further includes a source and a drain connected through contact features landing on the source and drain, respectively; a gate stack overlying a channel and interposed between the source and the drain; and a doped feature disposed underlying the channel and connecting to the source and the drain, wherein the doped feature is doped with a dopant of a same type of the source and the drain.

BACKGROUND

Along with the evolution of integrated circuits (IC) technology, it isexpected that the parasitic capacitance is reduced as less as possiblefor lower power and high speed. A decouple capacitance (de-cap) deviceis incorporated into the integrated circuits, such as logic circuits andanalog circuits, to reduce the parasitic capacitance. However, thede-cap device occupies a large circuit area, which negatively impactsde-cap device density and increases production cost. Especially, when ade-cap device is used in an analog circuit that is integrated with thelogic circuit and shares a same fabrication process, it occupies a largearea, and/or its capacitance cannot be increased cost-effectively. It istherefore desired to have a structure of an integrated circuit having ade-cap device and a method making the same to address the above issues.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a block view of an integrated circuit (IC) structure having ade-cap device constructed according to various aspects of the presentdisclosure in one embodiment.

FIG. 2 is a schematic view of a de-cap device of FIG. 1, constructedaccording to various aspects of the present disclosure in oneembodiment.

FIG. 3 is a sectional view of a de-cap device constructed according tovarious aspects of the present disclosure in one embodiment.

FIG. 4 is a sectional view of the de-cap device of FIG. 3 and aschematic view of the corresponding parasitic capacitance constructedaccording to various aspects of the present disclosure in oneembodiment.

FIG. 5 is a sectional view of a de-cap device constructed according tovarious aspects of the present disclosure in one embodiment.

FIG. 6 is a sectional view of a de-cap device constructed according tovarious aspects of the present disclosure in another embodiment.

FIG. 7 is a flowchart of a method making an integrated circuit structurehaving a de-cap device in accordance with various embodiments.

FIGS. 8 and 9 are top views of a mask structure used in the method ofFIG. 7 in accordance with various embodiments.

FIG. 10 is a sectional view of an IC structure having a de-cap devicewith various doping profiles in accordance with various embodiments.

FIG. 11 is a top view of an IC structure having a de-cap device inaccordance with various embodiments.

FIGS. 12, 13, 14, 15 and 16 are sectional views of the IC structurehaving a de-cap device of FIG. 11 at various fabrication stages inaccordance with various embodiments.

FIG. 17 is a flowchart of a method making an integrated circuit having ade-cap device structure of FIG. 15 or FIG. 16 in accordance with variousembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact.

In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “over,” “below,” “beneath,”“up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for easeof the present disclosure of one features relationship to anotherfeature. The spatially relative terms are intended to cover differentorientations of the device including the features. Still further, when anumber or a range of numbers is described with “about,” “approximate,”and the like, the term is intended to encompass numbers that are withina reasonable range including the number described, such as within +/−10%of the number described or other values as understood by person skilledin the art. For example, the term “about 5 nm” encompasses the dimensionrange from 4.5 nm to 5.5 nm.

The present disclosure provides various embodiments of an integratedcircuit (IC) structure having a decouple capacitance (de-cap) deviceformed on a semiconductor substrate and a method making the same.

FIG. 1A is a block view of an IC structure 50 in accordance with someembodiments. The IC structure 50 is formed on a semiconductor substrate.The IC structure 50 includes various circuit modules 52 integrated onthe same semiconductor substrate. For examples, the IC structure 50includes one or more logic circuit module, one or more analog circuitmodule, and other circuit modules, such as memory cells, imagingsensors, and etc.

The IC structure 50 also includes one or more de-cap device 54integrated with various circuit modules on the semiconductor substrate.In the present embodiment, the de-cap device 54 includes a transistor 56with a source and a drain connected to a power line 58, such as a groundline (Vss) and a gate connected to a complementary power line 59, suchas a high-power line (Vdd). Such configured device 54 functions as acapacitor for decoupling capacitance. The de-cap device 54, whenintegrated with other circuit modules, can provide various functions toenhance circuit performance, such as stabilization of the circuit. Forexample, the de-cap device 54 stabilizes the performance of transistorsdue to a lot of charges being stored in the de-cap device 54. Once thetransistors are operated in high speed, the de-cap device 54 can supplycharges faster than outside power, which catches up the time delay fromthe IR drop if the de-cap device is not presented.

FIG. 3 is a sectional view of a de-cap device 54 in accordance with someembodiments. The de-cap device 54 is formed on a semiconductor substrate60. The de-cap device 54 includes a field-effect transistor (FET) havinga source 62 and a drain 63 interposed by a gate stack 64. The FET may bea n-type FET or alternatively p-type FET. A gate spacer 68 is furtherdisposed on sidewalls of the gate stack 64. The gate stack 64 furtherincludes a gate dielectric layer 65 disposed on the semiconductorsubstrate 60 and a gate electrode 66 disposed on the gate dielectriclayer 65. The de-cap device 54 further includes a channel 69 underlyingthe gate electrode 66. The channel 69 is formed on active region of thesemiconductor substrate 60. The de-cap device 54 may further includevarious contact features 70 landing on the source 62 and the drain 63,respectively. The source 62 and the drain 63 are electrically connected,such as through various conductive features (including contact features70) of an interconnection structure.

FIG. 4 is a sectional view of the de-cap device 54 with schematic viewof parasitic capacitance of the de-cap device 54 constructed inaccordance with some embodiments. The de-cap device 54 includes a firstparasitic capacitance C₁ between the channel 69 and the gate electrode66 with the gate dielectric layer 65 configured therebetween. The de-capdevice 54 further includes a second parasitic capacitance C₂ between thecontact feature 70 of the source 62 and the gate electrode 66; and athird parasitic capacitance C₃ between the contact feature 70 of thedrain 63 and the gate electrode 66. In some embodiments where the gatestack is extended into deep into the semiconductor substrate 60, such asgate-all-around FET device, which will be further described in detaillater, the de-cap device 54 further includes a fourth parasiticcapacitance C₄ between the source 62 and the gate electrode 66; and afifth parasitic capacitance C₅ between the drain 63 and the gateelectrode 66.

FIG. 5 is a sectional view of a de-cap device 54 constructed inaccordance with some embodiments. The de-cap device 54 is formed on asemiconductor substrate 60. The de-cap device 54 includes a field-effecttransistor (FET) having a source 62 and a drain 63 interposed by a gatestack 64. A gate spacer 68 is disposed on sidewalls of the gate stack66. The gate stack 64 further includes a gate dielectric layer 65disposed on the semiconductor substrate 60 and a gate electrode 66disposed on the gate dielectric layer 65. The de-cap device 54 furtherincludes a channel 69 underlying the gate electrode 66. The channel 69is formed on active region of the semiconductor substrate 60. The de-capdevice 54 may further include various contact features 70 landing on thesource 62 and the drain 63, respectively. The source 62 and the drain 63are electrically connected together by various conductive features, suchas contact features 70, via features 72 and a metal line 74, of aninterconnection structure 76. The gate stack 64 and the interconnectionstructure 76 are formed in one or more interlayer dielectric (ILD) layer78.

Particularly, the de-cap device 54 includes a doped feature 80 disposedin the semiconductor substrate 60. The doped feature 80 is disposedunder the channel 69. In the present embodiment, the doped feature 80contacts the bottom surfaces of the source 62 and the drain 63 andtherefore is connected to the source 62 and the drain 63. The dopedfeature 80 is different from an anti-punch-through (APT) doped feature.The APT doped feature is doped with a type opposite to that of thesource 62 and the drain 63. However, the doped feature 80 is doped witha same type of the source 62 and the drain 63. For example, when the FETof the de-cap device 54 is an n-type FET, the source 62 and the drain 63are doped with a n-type dopant while the doped feature 80 is doped withan n-type dopant as well. Therefore, the doped feature 80 is alsoreferred to as a reverse APT doped feature 80. The reversed APT feature80 renders the bottom surface of the channel to the gate stack 64planar, thereby increasing the capacitance of the de-cap device 54. Thereversed APT feature 80 raises up the inversion voltage and renders ithard to inverse (or deplete), therefore eliminating or reducing theleakage path at sub-channel. If it is depleted, there would be nocapacitance thereby. The reversed APT feature makes the bottom channelfrom depletion state to normally no-depletion state to gain thecapacitance. In some embodiments as noted above, the de-cap device 54functions as a capacitor and includes a capacitor between the gateelectrode 66 and the channel 69 with the source 62 and the drain 63connected together. However, the connection between the source 62 andthe drain 63 is getting weak due to the voltage drop from the resistanceof various components, such as the contact features 70, the source 62and the drain 63. The reversed APT doped feature 80 further connects thesource 62 and the drain 63 from the bottom in addition to the connectionthrough the contact features 70 on the top, which may additionally gaincapacitance accordingly.

Still referring to FIG. 5, the de-cap device 54 may be formed in a finactive region 82 extruded above the semiconductor substrate 60. Thesemiconductor substrate 60 includes various isolation features 84 toprovide isolation function. The fin active regions 82 are surrounded bythe isolation features 84 and are extruded above the isolation features84. The top surface 82A of the fin active region 82 is above the topsurface 84A of the isolation feature 84 with a fin height Hf. In someembodiments, the isolation features 84 include shallow-trench isolation(STI) features. The isolation feature 84 includes silicon oxide, siliconnitride, silicon oxynitride, other suitable dielectric materials, orcombinations thereof. The isolation feature 84 is formed by any suitableprocess. As one example, forming STI features includes a lithographyprocess to expose a portion of the substrate, etching a trench in theexposed portion of the substrate (for example, by using a dry etchingand/or wet etching), filling the trench (for example, by using achemical vapor deposition process) with one or more dielectricmaterials, and planarizing the substrate and removing excessive portionsof the dielectric material(s) by a polishing process, such as a chemicalmechanical polishing (CMP) process. In some examples, the filled trenchmay have a multi-layer structure, such as a thermal oxide liner layerand filling layer(s) of silicon nitride or silicon oxide.

The semiconductor substrate 60 includes silicon. Alternatively, thesubstrate 60 may include an elementary semiconductor, such as silicon orgermanium in a crystalline structure; a compound semiconductor, such assilicon germanium, silicon carbide, gallium arsenic, gallium phosphide,indium phosphide, indium arsenide, and/or indium antimonide; orcombinations thereof. Possible substrates 60 also include asilicon-on-insulator (SOI) substrate. SOI substrates are fabricatedusing separation by implantation of oxygen (SIMOX), wafer bonding,and/or other suitable methods.

FIG. 6 is a sectional view of a de-cap device 54 constructed inaccordance with some embodiments. The de-cap device 54 is formed on asemiconductor substrate 60. The de-cap device 54 includes ananostructure, such as a nanowire, nanosheet or other suitablenanostructures. In the present embodiment, the de-cap device 54 includesa gate-all-around (GAA) FET structure having a source 62 and a drain 63interposed by a gate stack 64. A gate spacer 68 is further disposed onsidewalls of the gate stack 64. The gate stack 64 further includes agate dielectric layer 65 disposed on the semiconductor substrate 60 anda gate electrode 66 disposed on the gate dielectric layer 65. The de-capdevice 54 further includes a plurality of channels (or channel regions)86 vertically stacked on the semiconductor substrate 60. The source 62and the drain 63 extend down to connect with each of the plurality ofchannels 86. Particularly, the gate dielectric layer 65 surrounds eachof the plurality of channels 86 and the gate electrode 66 surrounds eachof the plurality of channels 86 interposed by the gate dielectric layer65. The de-cap device 54 may further include various contact features 70landing on the source 62 and the drain 63, respectively. The source 62and the drain 63 are electrically connected together by variousconductive features, such as contact features 70, via features 72 and ametal line 74, of an interconnection structure 76. The de-cap device 54further includes a doped feature 80 disposed below the plurality ofchannels 86. The doped feature 80 is disposed below the source 62 andthe drain 63. In the present embodiment, the doped feature 80 isconfigured to contact the bottom surfaces of the source 62 and the drain63. In various embodiments, the channels 86 may include one or moresemiconductor material same or different from the semiconductor materialof the semiconductor substrate 60, such as silicon, germanium, silicongermanium, silicon carbide or other suitable semiconductor materials.

The formation of the de-cap device 54 or the IC structure 50 is furtherdescribed with reference to FIG. 7 as a flowchart of a method 100constructed in accordance with some embodiments and with furtherreference FIGS. 1, 5 and 6. The de-cap device 54 includes a fin FET 56as illustrated in FIGS. 1 and 5, or a GAA-FET structure as illustratedin FIG. 6, according to various embodiments. The present disclosure isnot limited to any particular number of devices or device regions, or toany particular device configurations. For example, though the ICstructure 50 as illustrated in FIG. 6 is a GAA-FET structure, thepresent disclosure may also provide embodiments for fabricating otherthree-dimensional FET devices, such as a fin FET (FinFET) structure. Invarious embodiments, the IC structure 50 may include a GAA FET structurewith a plurality of FETs stacked on, such as p-type FETs (PFETs), n-typeFETs (NFETs), fin-like FETs (FinFETs), metal-oxide semiconductor fieldeffect transistors (MOSFET), complementary metal-oxide semiconductor(CMOS) transistors, bipolar transistors, high voltage transistors, highfrequency transistors, and/or other memory cells. In various examples,the IC structure 50 may include logic circuits, memory circuits, such asstatic random-access memory (SRAM), and/or other suitable circuitshaving active components (such as transistors, diodes, and imagingsensors) and passive components (such as resistors, capacitors, andinductors). The IC structure 50 may be an intermediate device fabricatedduring processing of an integrated circuit (IC), or a portion thereof.

The method 100 includes a block 101 by receiving a workpiece having asemiconductor substrate 60. As described earlier, the semiconductorsubstrate 60 includes one or more semiconductor material, such assilicon. Alternatively, the semiconductor substrate 60 may include anelementary semiconductor, such as silicon or germanium in a crystallinestructure; a compound semiconductor, such as silicon germanium, siliconcarbide, gallium arsenic, gallium phosphide, indium phosphide, indiumarsenide, and/or indium antimonide; or combinations thereof. Possiblesubstrates 60 may also include a silicon-on-insulator (SOI) substrate.SOI substrates are fabricated using separation by implantation of oxygen(SIMOX), wafer bonding, and/or other suitable methods. In someembodiments associated with the de-cap device 54 having a GAA-FET, suchas de-cap device 54 in FIG. 6, the semiconductor substrate 60 includes astack of alternating a first semiconductor (such as silicon (Si)) filmsand a second semiconductor (such as silicon germanium (SiGe)) filmsepitaxially grown on the silicon substrate 60. During a wire-releaseprocess, one type of films, such as SiGe films, are selectively removed,another type of films, such as Si films, are patterned to form aplurality of channels 86 vertically stacked.

The method 100 may include other operations, such as an operation 102 toform various doping features, such as doped wells and channel 69 in FIG.5 or a plurality of channels 86 in FIG. 6, by proper processes, such asion implantations.

The Method 100 includes an operation 103 to form a reversed APT dopedfeature 80 underlying the channel 69 (in FIG. 5) or underlying theplurality of channels 86 (in FIG. 6). In the present embodiment, thereversed APT doped feature 80 connects to the source 62 and the drain63. In furtherance of the embodiment, the reversed APT doped feature 80contacts to the bottom surface of the source 62 and the drain 63. Thereversed APT doped feature 80 has a same type of dopant of the source 62and the drain 63 while an APT doped feature has a doping type oppositeto that of the source 62 and the drain 63.

Thus, the reversed APT doped feature 80 of a p-type FET (or a p-typeGAA-FET) can be simultaneously formed with a APT doped feature of an-type FET (or a n-type GAA-FET) by a same process, such as an ionimplantation process without increasing the fabrication cost, asillustrated in FIG. 8. FIG. 8 is a photomask 200 used in a lithographyprocess to form a patterned resist layer to define regions for APT dopedfeatures and the reversed APT doped features 80. When the IC structure50 includes a region for p-type FETs (or p-type GAA-FETs, collectivelyreferred to as “P-FET region”); a region for n-type FETs (or n-typeGAA-FETs, collectively referred to as “N-FET region”); and a region fora de-cap device 54 including a p-type FET (or a p-type GAA-FET,collectively referred to as “De-cap region”), the photomask 200 includesa pattern with openings aligned to the N-FET region and De-cap regionwhile the P-FET region is covered. Accordingly, the resist layer coatedon the workpiece is patterned by a lithography process that includes anexposure process using the photomask 200 and a developing process. Thepatterned resist layer may be transferred to a hard mask using as an ionimplantation mask. Then an ion implantation process is performed throughthe openings of the patterned resist layer (or of the hard mask) tointroduce p-type dopant (such as boron) into the active regions belowthe channels, thereby forming the reversed APT doped feature 80 to thede-cap device 54 in the De-cap region and the APT doped feature to then-type FETs in the N-FET region with a same doping profile.

Similarly, the reversed APT doped feature 80 of a n-type FET (or an-type GAA-FET) can be simultaneously formed with a APT doped feature ofa p-type FET (or a p-type GAA-FET) by a same process, such as an ionimplantation process, as illustrated in FIG. 9. FIG. 9 is a photomask202 used in a lithography process to form a patterned resist layer todefine regions for APT doped features and the reversed APT dopedfeatures 80. When the IC structure 50 includes a region for n-type FETs(or n-type GAA-FETs, collectively referred to as “N-FET region”); aregion for p-type FETs (or p-type GAA-FETs, collectively referred to as“P-FET region”); and a region for a de-cap device 54 including a n-typeFET (or a n-type GAA-FET, collectively referred to as “De-cap region”),the photomask 200 includes a pattern with openings aligned to the P-FETregion and De-cap region while the N-FET region is covered. Accordingly,the resist layer coated on the workpiece is patterned by a lithographyprocess that includes an exposure process using the photomask 202 and adeveloping process. The patterned resist layer may be transferred to ahard mask using as an ion implantation mask. Then an ion implantationprocess is performed through the openings of the patterned resist layer(or of the hard mask) to introduce n-type dopant (such as phosphorous)into the active regions below the channels, thereby forming the reversedAPT doped feature 80 to the de-cap device 54 in the De-cap region andthe APT doped feature to the p-type FETs in the P-FET region with a samedoping profile.

Various doped features, especially the reversed APT doped feature 80,are further described with reference to FIG. 10. FIG. 10 is a sectionalview of the IC structure 50, in portion, constructed in accordance withsome embodiments. The IC structure 50 includes a circuit module 52(e.g., or a logic circuit) and a de-cap device 54, each including aGAA-FET, which further includes a doped well (“Well”) and doped source62 and drain 63. Particularly, the GAA-FET of the circuit module 52includes an APT doped feature (“APT) while the GAA-FET of the de-capdevice 54 includes a reversed APT doped feature 80 below the source 62and the drain 63.

In some embodiments, the GAA-FETs in the circuit module 52 is n-type andthe GAA-FETs in the de-cap device 54 is p-type. In this case, dopingtypes and doping concentrations are as follow. For the GAA-FETs in thecircuit module 52, the source 62 and the drain 63 are doped with an-type dopant (such as phosphorous); and the well is doped with a p-typedopant. Especially, the source 62 and the drain 63 include twoepitaxially grown semiconductor layers L₁ and L₂ with different dopingconcentrations. The first semiconductor layer L₁ includes a n-typedopant (such as phosphorous) with a doping concentration ranging between10²⁰/cm³ and 10²¹/cm³; and the second semiconductor layer L₂ includes an-type dopant (such as phosphorous) with a doping concentration rangingbetween 10²¹/cm³ and 8×10²¹/cm³; and the APT doped feature includes ap-type dopant (such as boron) with a doping concentration rangingbetween 2×10¹³/cm³ and 10¹⁴/cm³. For the GAA-FETs in the de-cap device54, the source 62 and the drain 63 are doped with a p-type dopant (suchas boron); and the well is doped with a n-type dopant. Especially, thesource 62 and the drain 63 include two epitaxially grown semiconductorlayers L₁ and L₂ with different doping concentrations. The firstsemiconductor layer L₁ includes a p-type dopant (such as boron) with adoping concentration ranging between 10²⁰/cm³ and 10²¹/cm³; and thesecond semiconductor layer L₂ includes a p-type dopant (such as boron)with a doping concentration ranging between 10²¹/cm³ and 8×10²¹/cm³; andthe APT doped feature 80 includes a p-type dopant (such as boron) with adoping concentration ranging between 2×10¹³/cm³ and 10¹⁴/cm³. Thereversed APT doped feature 80 of a p-type GAA-FETs in the de-cap device54 and the APT doped feature of a n-type GAA-FETs in the circuit module52 have a same doping type and a same doping profile. Accordingly, bothcan be formed by a same ion implantation process using a same photomaskas described in FIG. 8.

In some embodiments, the GAA-FETs in the circuit module 52 is p-type andthe GAA-FETs in the de-cap device 54 is n-type. In this case, dopingtypes and doping concentrations are as follow. For the GAA-FETs in thecircuit module 52, the source 62 and the drain 63 are doped with an-type dopant (such as phosphorous); and the well is doped with a p-typedopant. Especially, the source 62 and the drain 63 include twoepitaxially grown semiconductor layers L₁ and L₂ with different dopingconcentrations. The first semiconductor layer L₁ includes a p-typedopant (such as boron) with a doping concentration ranging between10²⁰/cm³ and 10²¹/cm³; and the second semiconductor layer L₂ includes ap-type dopant (such as boron) with a doping concentration rangingbetween 10²¹/cm³ and 8×10²¹/cm³; and the APT doped feature includes an-type dopant (such as phosphorous) with a doping concentration rangingbetween 2×10¹³/cm³ and 10¹⁴/cm³. For the GAA_FET in the de-cap device54, the source 62 and the drain 63 are doped with a n-type dopant (suchas phosphorous); and the well is doped with a p-type dopant. Especially,the source 62 and the drain 63 include two epitaxially grownsemiconductor layers L₁ and L₂ with different doping concentrations. Thefirst semiconductor layer L₁ includes a n-type dopant (such asphosphorous) with a doping concentration ranging between 10²⁰/cm³ and10²¹/cm³; and the second semiconductor layer L₂ includes a n-type dopant(such as phosphorous) with a doping concentration ranging between10²¹/cm³ and 8×10²¹/cm³; and the APT doped feature 80 includes a n-typedopant (such as phosphorous) with a doping concentration ranging between2×10¹³/cm³ and 10¹⁴/cm³. The reversed APT doped feature 80 of a n-typeGAA-FET in the de-cap device 54 and the APT doped feature of a n-typeGAA-FET in the circuit module 52 have a same doping type and a samedoping profile. Accordingly, both can be formed by a same ionimplantation process using a same photomask as described in FIG. 9.Alternatively, the reversed APT doped feature 80 includes carbon asdopant with a doping concentration ranging between 2×10¹³/cm³ and10¹⁴/cm³. In the present embodiment, the source 62 and the drain 63include a height H₁ ranging between 50 nm and 55 nm; and the reversedAPT doped feature 80 and the APT doped feature include a height H₂ranging between 20 nm and 35 nm.

The Method 100 includes an operation 104 to form isolation features(isolation structures), such as isolation features 84 in FIG. 5. Theisolation features 84 may include silicon oxide, silicon nitride,silicon oxynitride, fluoride-doped silicate glass (FSG), a low-kdielectric material, and/or other suitable materials. The isolationfeatures 84 may include shallow trench isolation (STI) features. In oneembodiment, the isolation features 84 are formed by etching trenches inthe substrate 60; filling the trenches with one or more dielectricmaterial described above by a deposition process; and followed by achemical mechanical planarization (CMP) process. Other isolationfeatures such as field oxide, local oxidation of silicon (LOCOS), and/orother suitable structures may also be implemented as the isolationfeatures 84. Alternatively, the isolation features 84 may include amulti-layer structure, for example, having one or more thermal oxideliner layers. The isolation features 84 may be deposited by any suitablemethod, such as chemical vapor deposition (CVD), flowable CVD (FCVD),spin-on-glass (SOG), high-density plasma CVD (HDPCVD), high aspect ratioprocess (HARP), other suitable methods, or combinations thereof.

In some embodiments, the method 100 may include an operation 106 to formthe fin active regions 82. In the operation 106, the isolation features84 may be subsequently recessed (e.g., by etch-back) such that a topsurface 84A of the isolation features 84 is below a top surface 82A ofthe fin active region 82, defining a fin height H_(f) of the fin activeregion 82 for optimized coupling between the gate electrode and thechannel. In some embodiments, the fin height of the semiconductor fins204 ranges between 50 nm and 70 nm.

The method 100 includes an operation 108 to form dummy gate stacks to bereplaced by metal gate stacks 64 at later stage. The formation of thedummy gate stacks includes deposition (such as depositing poly-siliconby CVD) and patterning, which further includes a lithography process andetching. In the present embodiment, the operation 108 further includesforming gate spacer 68 on sidewalls of the dummy gate stacks. The gatespacer 68 includes one or more dielectric material, such as siliconoxide, silicon nitride, silicon oxynitride or a combination thereof. Theformation of the gate spacer 68 includes deposition (such as CVD) andanisotropic etching (such as plasma etching).

The method 100 includes an operation 110 to form source 62 and drain 63on the fin active region 82 within the source/drain regions. In theoperation 110, the source/drain (S/D) regions may be recessed byetching. In some embodiments, a hard mask having openings that exposethe S/D regions may be used as an etch mask. A suitable etching process,such as a dry etching process, a wet etching process, an RIE process, ora combination thereof may be used to recess the S/D regions. The etchingprocess at operation 110 may implement a dry etching process using anetchant including a bromine-containing gas (e.g., HBr and/or CHBR₃), afluorine-containing gas (e.g., CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆),other suitable gases, or combinations thereof. The extent of which thefin active regions 82 within the S/D regions is removed may becontrolled by adjusting the duration of the etching process. In someembodiments associated with the de-cap device 54 of FIG. 6, therecessing depth extends to whole thickness of the alternativeepitaxially grown semiconductor layers.

The operation 110 also includes epitaxially growing a semiconductormaterial to fill in the recesses, thereby forming source 62 and drain 63(or collectively referred to as S/D features). The S/D feature mayinclude multiple epitaxial semiconductor layers, such as with differentsemiconductor composition, with different doping concentrations, or acombination thereof. For example, the S/D features includes a firstsemiconductor material layer with a first doping concentration; and asecond semiconductor material layer disposed on the first semiconductorlayer and having a second first doping concentration greater than thefirst doping concentration. In the present embodiment, the dopant isin-situ introduced into the S/D features during the selective epitaxialgrowth. The operation 110 may include other processing steps. Forexample, for the de-cap device 54 of FIG. 6, the operation 110 mayinclude laterally etching in the recesses to selectively remove portionsof one type of the alternative semiconductor material layers; anddepositing dielectric material and etching to form inner spaces near thechannels before the selective epitaxial growth.

The method 100 also includes an operation 112 to form an inter-layerdielectric (ILD) layer 78 on the workpiece to provide isolationfunctions among various conductive features. The ILD layer 78 includesone or more dielectric material and may be formed by deposition and CMP.The ILD layer 78 includes one or more dielectric material, such assilicon oxide, tetraethylorthosilicate (TEOS), un-doped silicate glass,or doped silicon oxide such as borophosphosilicate glass (BPSG), fusedsilica glass (FSG), phosphosilicate glass (PSG), boron doped siliconglass (BSG), low-k dielectric material or other suitable dielectricmaterial. In various embodiments, the ILD layer 78 is deposited by CVD,HDPCVD, sub-atmospheric CVD (SACVD), HARP, a flowable CVD (FCVD), and/ora spin-on process. In some embodiments, forming the ILD layer 78 furtherincludes performing a CMP process to planarize such that the topsurfaces of the dummy gate stacks are exposed. In some embodiments, abottom contact etch-stop layer (BCESL) may be deposited under the ILDlayer 78 with a different composition, such as silicon nitride, toachieve etch selectivity. The BCESL is conformally deposited on thesource 62, the drain 63 and the dummy gate stacks.

The method 100 includes an operation 114 to remove the dummy gate stack,partially or completely by etch, resulting in a gate trench in the ILDlayer 78. The operation 114 may additionally include patterning withphotolithography process. For example, the dummy gate stack for ann-type FET is removed by an etching process with a hard mask to coverthe region for a p-type FET; and the dummy gate stack for the p-type FETis removed by another etching process with another hard mask to coverthe region for the n-type FET in order to fill them separately withdifferent material, such as different metals with respective workfunctions to reduce the threshold voltages. Forming the gate trench mayinclude one or more etching processes that are selective to thematerials included in the dummy gate stacks (e.g., polysiliconincluded). The etching processes may include dry etching, wet etching,RIE, or other suitable etching methods, or combinations thereof.

In the de-cap device 54 associated with FIG. 6, the method 100 alsoincludes an operation 116 to perform an etching process to selectivelyremove the second semiconductor films in the gate trench to form gapsbetween layers of the first semiconductor films, such that portions ofthe first semiconductor material suspend in space with gaps among thestacked first semiconductor materials, functioning as channels 86 to thecorresponding GAA-FET devices. As discussed above, the firstsemiconductor films include Si and the second semiconductor filmsinclude SiGe. Accordingly, the etching process at operation 116selectively removes portions of SiGe without removing or substantiallyremove Si. In some embodiments, the etching process is an isotropicetching process (e.g., a dry etching process or a wet etching process).In an example embodiment, the operation 116 selectively removes portionsof the second semiconductor films by a wet etching process that utilizesHF and/or NH₄OH as an etchant, which initially oxidizes portions of thesecond semiconductor films to form SiGeOx and subsequently removes theSiGeOx by etch. The operation 116 may be implemented at other properfabrication stage to form the channels 86.

In some embodiments, the method 100 may include an operation to convertthe channels 86 into a different semiconductor material, such as forstrain effect. In one example, the first semiconductor films areconverted from silicon into silicon germanium. This can be achieved by asuitable method, such as an ion implantation to introduce germanium intothe channels 86. Alternatively, the operation 116 removes the secondsemiconductor films, leaving a portion on the first semiconductor films.An annealing process is applied subsequently to drive germanium from theremaining portion of the second semiconductor films into the firstsemiconductor films. In some embodiments, the channels 86 may havedifferent shapes in section view, such as a round shape, an ellipticalshape, or an olive shape for GAA-FETs with a nanochannel structure, asillustrated in FIG. 6.

The method 100 proceeds to an operation 118 to form a metal gate stack64 in the gate trench. In some embodiments, the metal gate stack 64includes a gate dielectric layer 65 having a high-k dielectric materialwith a dielectric constant greater than that of silicon dioxide (about3.9); and a gate electrode 66 having a metal or metal alloy. Theformation of the metal gate stack 64 includes depositing various gatematerials (including gate dielectric material and gate electrodematerial) and CMP. During the operation 118, various material layers ofthe metal gate stack 64 are deposited in the gate trench formed betweenthe layers of the first semiconductor material. The gate dielectriclayer may further include an interfacial (IF) layer (such as siliconoxide) underlying the high-k dielectric material. Though not depicted,the metal electrode may include multiple metal or metal alloy layers,such as a work function metal layer formed over the high-k dielectricmaterial layer, a bulk conductive layer formed over the work functionmetal layer, other suitable layers, or combinations thereof. The high-kdielectric material may include one or more high-k dielectric materials(or one or more layers of high-k dielectric materials), such as hafniumsilicon oxide (HfSiO), hafnium oxide (HfO₂), alumina (Al₂O₃), zirconiumoxide (ZrO₂), lanthanum oxide (La₂O₃), titanium oxide (TiO₂), yttriumoxide (Y₂O₃), strontium titanate (SrTiO₃), or a combination thereof. Thework function metal layer may include any suitable material, such astitanium nitride (TiN), tantalum nitride (TaN), ruthenium (Ru),molybdenum (Mo), tungsten (W), platinum (Pt), titanium (Ti), aluminum(Al), tantalum carbide (TaC), tantalum carbide nitride (TaCN), tantalumsilicon nitride (TaSiN), titanium silicon nitride (TiSiN), othersuitable materials, or combinations thereof. In some embodiments, thework function metal layer includes multiple material layers of the sameor different types (i.e., both n-type work function metal or both p-typework function metal) in order to achieve a desired threshold voltage.The bulk conductive layer may include aluminum (Al), copper (Cu),tungsten (W), cobalt (Co), ruthenium (Ru), other suitable conductivematerials, or combinations thereof. The metal gate structure 64 mayinclude other material layers, such as a barrier layer, a glue layer,and/or a capping layer. The various layers of the metal gate stack 64may be formed by any suitable method, such as CVD, ALD, PVD, plating,chemical oxidation, thermal oxidation, other suitable methods, orcombinations thereof. Thereafter, the method 100 may perform one or morepolishing process (e.g., CMP) to remove any excess conductive materialsand planarize the top surface of the IC structure 50.

The method 100 may include an operation 120 to form S/D contact features70 landing on the source 62 and the drain 63 to be in electrical contactwith the corresponding the source 62 and the drain 63. Each contactfeature may include one or more conductive layers and may be formed by aprocedure that includes patterning to form a contact hole in the ILDlayer 78, and deposition to fill the contact hole with one or moreconductive material. The patterning process includes photolithographyprocess and etching. The deposition may use any suitable method such asALD, CVD, PVD, plating, and/or other suitable processes. In someembodiments, each S/D contact feature 70 includes a seed metal layer anda fill metal layer. In various embodiments, the seed metal layerincludes cobalt (Co), tungsten (W), ruthenium (Ru), nickel (Ni), othersuitable metals, or combinations thereof. The fill metal layer mayinclude copper (Cu), tungsten (W), aluminum (Al), cobalt (Co), othersuitable materials, or combinations thereof.

Referring to FIG. 7, the method 100 at operation 122 may performadditional processing steps. For example, additional verticalinterconnect features such as vias, horizontal interconnect featuressuch as lines, and/or multilayer interconnect features such as metallayers and interlayer dielectrics can be formed over the semiconductorsubstrate 60. The various interconnect features may implement variousconductive materials including copper (Cu), tungsten (W), cobalt (Co),aluminum (Al), titanium (Ti), tantalum (Ta), platinum (Pt), molybdenum(Mo), silver (Ag), gold (Au), manganese (Mn), zirconium (Zr), ruthenium(Ru), their respective alloys, metal silicides, other suitablematerials, or combinations thereof. The metal silicides may includenickel silicide, cobalt silicide, tungsten silicide, tantalum silicide,titanium silicide, platinum silicide, erbium silicide, palladiumsilicide, other suitable metal silicides, or combinations thereof.

In summary, the present disclosure provides a method to form an ICstructure 50 having a de-cap device 54 that includes a FET, a FinFET ora GAA-FET structure having the source and the drain connected from thetop through the interconnection structure and from the bottom throughthe reversed APT doped feature, which increases capacitance of thede-cap device, reduces the occupying area of the de-cap device 54, andenhances the circuit performance of the IC structure.

FIG. 11 is a top view an IC structure 300, in portions, FIGS. 12-16 aresectional views of an IC structure 300, in portions, along the dashedline AA′ at various fabrication stages, constructed in accordance withsome embodiments. The IC structure 300 includes a circuit module 52 anda de-cap device 54 integrated in a semiconductor substrate. FIG. 17 is aflowchart of a method 400 making the IC structure 300. The method 400and the IC structure 300 are collective described with reference toFIGS. 11-17. The IC structure 300 is similar to the IC structure 50.Particularly, the de-cap device 54 includes a FET (FinFET or GAA-FET)with the source 62 and the drain 63 connected through the contactfeatures 70 and may additionally connected through a reversed APT dopedfeature 80. However, the isolation features 84 in the circuit module 52and the de-cap device 54 are different in height. Similar components andprocessing steps making the same are not repeated below.

Especially, the operation 104 forms isolation features, such as STIfeatures, by a procedure that includes patterning the ILD layer 78 toform a trench; depositing one or more dielectric material to fill thetrench; performing a CMP process to remove the excessive dielectricmaterial above the trench; and performing a first recessing process torecess the dielectric material, thereby forming the isolation features84 and fin active regions 82, as illustrated in FIG. 12.

The method 400 further includes an operation 402 to perform a secondrecessing process to further recess the STI features 84 in the de-capdevice region, thereby reducing the isolation features 84 in the de-capdevice region to the isolation features 306 with less thickness, asillustrated in FIG. 14. In some embodiments, the operation 402 mayinclude forming a patterned mask 302 with openings (in FIG. 13); andperforming the second recessing process 304 through the openings of thepatterned mask 302 (in FIG. 14). The patterned mask 302 may be a softmask, such as a patterned resist layer formed by a lithography process,or a hard mask formed by etching to transfer the openings from thepatterned resist layer to the hard mask. The patterned mask 302 coversthe regions for the circuit module 52 and includes the openings toexpose the regions for the de-cap device 54. The second recessingprocess 304 may include etching, such as dry etching, wet etching or acombination thereof.

Such formed IC structure 300 is further illustrated in FIG. 15. In thepresent embodiment, the circuit module 52 includes two exemplary finactive regions 82 (such as one for n-type FET and another for p-typeFET); and the de-cap device 54 includes two exemplary fin active regions82 as well (such as one for n-type FET and another for p-type FET). Theisolation features 306 includes a thickness T₁ less than that of theisolation features 84 by T₂. In some examples, T₁ ranges between 30 nmand 40 nm and T₂ ranges between 20 nm and 30 nm.

The FET structure is illustrated only as one embodiment. The method 400can also be used to form the IC structure 300 with the de-cap device 54having a GAA-FET structure as illustrated in FIG. 16. In this case, thechannels 86 are formed by a wire-release process in the operation 116.Since the isolation features 306 has a reduced thickness, thecorresponding capacitance of the de-cap device 54 is increasedaccordingly, therefore increasing the capacitance without increasing thedevice area. In some embodiments, this reduced isolation features 306are further combined with the reversed APT doped feature 80 tocollectively increasing the capacitance of the de-cap device 54 withoutincreasing the device area and the fabrication cost.

The present disclosure provides various embodiments of an IC structurehaving a circuit module and a de-cap device integrated together. Thede-cap device includes a FET structure, such as a FinFET structure or aGAA-FET structure. The de-cap device includes a source and a drainelectrically connected through S/D contact features and a reversed APTdoped feature connecting to the source and drain. Especially, thereversed APT doped feature includes a dopant of a same type to thedopant of the source and drain. In some embodiment, the isolationfeatures (such as STI features) surrounding the de-cap device is furtherrecessed relative to the STI features in the region for the circuitmodule (such as a logic circuit, an analog circuit or a combinationthereof) to increase the capacitance of the de-cap device withoutincreasing the device area. In some embodiments, this reduced isolationfeatures are further combined with the reversed APT doped feature tocollectively increasing the capacitance of the de-cap device withoutincreasing the device area and the fabrication cost.

In one aspect, the present disclosure provides an integrated circuitthat includes a circuit formed on a semiconductor substrate; and ade-cap device formed on the semiconductor substrate and integrated withthe circuit. The de-cap device includes a filed-effect transistor (FET)that further includes a source and a drain connected through contactfeatures landing on the source and drain, respectively; a gate stackoverlying a channel and interposed between the source and the drain; anda doped feature disposed underlying the channel and connecting to thesource and the drain, wherein the doped feature is doped with a dopantof a same type of the source and the drain.

In another aspect, the present disclosure provides a method thatincludes forming a source and a drain on a semiconductor substrate,wherein the source and the drain are doped with a first-typeconductivity; forming a channel doped of a second-type conductivitybeing opposite to the first-type conductivity; forming a doped featureof the first-type conductivity, wherein the doped feature is underlyingthe channel and connects the source and the drain; and forming a gatestack that includes forming a gate dielectric layer and a gateelectrode, wherein the source, the drain, the channel and the gate stackare components of a de-cap device having the source and the drainconnected through an interconnection structure.

In yet another aspect, the present disclosure provides an integratedcircuit that includes a first fin active region and a second fin activeregion on a semiconductor substrate; a first sallow-trench isolation(STI) feature surrounding the first fin active region; a secondsallow-trench isolation (STI) feature surrounding the second fin activeregion, the first STI feature includes a top surface above a top surfaceof the second STI feature and below a top surface of the first andsecond fin active regions; a circuit having a first field-effecttransistor (FET) formed on the first fin active region; and a de-capdevice formed on the second fin active region, wherein the de-cap deviceincludes a second FET that further includes a source and a drainconnected through contact features landing on the source and drain,respectively, and a gate stack interposed between the source and thedrain.

The foregoing has outlined features of several embodiments. Thoseskilled in the art should appreciate that they may readily use thepresent disclosure as a basis for designing or modifying other processesand structures for carrying out the same purposes and/or achieving thesame advantages of the embodiments introduced herein. Those skilled inthe art should also realize that such equivalent constructions do notdepart from the spirit and scope of the present disclosure, and thatthey may make various changes, substitutions and alterations hereinwithout departing from the spirit and scope of the present disclosure.

What is claimed is:
 1. An integrated circuit, comprising: a circuitformed on a semiconductor substrate; and a de-cap device formed on thesemiconductor substrate and integrated with the circuit, wherein thede-cap device includes a filed-effect transistor (FET) that furtherincludes a source and a drain connected through contact features landingon the source and drain, respectively, a channel spanning between thesource and the drain, a gate stack overlying the channel and interposedbetween the source and the drain, and a doped feature disposedunderlying the channel and connecting to the source and the drain,wherein the doped feature is doped with a dopant of a same type of thesource and the drain, and wherein the channel is doped with a dopantopposite to that of the doped feature.
 2. The integrated circuit ofclaim 1, further comprising a fin active region in the semiconductorsubstrate; a shallow trench isolation (STI) feature formed on thesemiconductor substrate and surrounding the fin active region, a topsurface of the fin active region above a top surface of the STI feature;and the source, the drain, the channel and the gate stack of the FET areformed on the fin active region.
 3. The integrated circuit of claim 2,wherein the FET is a n-type FET, the source and the drain are n-typedoped, and the doped feature is n-type doped.
 4. The integrated circuitof claim 3, wherein the circuit further includes a p-type FET having ananti-punch-through (APT) feature that is n-type doped, wherein the APTfeature has a first doping concentration less than 1×10¹⁴/cm³; each ofthe source and the drain includes a second doping concentration greaterthan 1×10²¹/cm³; and the doped feature includes a third dopingconcentration being equal to the first doping concentration.
 5. Theintegrated circuit of claim 4, wherein the fin active region is a firstfin active region and the STI feature is a first STI feature, whereinthe n-type FET is disposed on the first fin active region surrounded bythe first STI feature, the p-type FET is disposed on a second fin activeregion surrounded by a second STI feature, and the second STI featureincludes a top surface above the top surface of the first STI feature.6. The integrated circuit of claim 2, wherein the FET is a p-type FET;the source and the drain are p-type doped; and the doped feature isp-type doped.
 7. The integrated circuit of claim 6, wherein the circuitfurther includes a n-type FET having an APT feature that is p-typedoped, wherein the APT feature has a first doping concentration lessthan 1×10¹⁴/cm³; each of the source and the drain includes a seconddoping concentration greater than 3×10²⁰/cm³; and the doped featureincludes a third doping concentration being equal to the first dopingconcentration.
 8. The integrated circuit of claim 1, wherein the FET isa gate-all-around FET (GAA-FET) including a plurality of channelsvertically stacked on the semiconductor substrate, the gate stack isextended to be around each of the plurality of channels, each of thesource and the drain extends down to be connected to the each of theplurality of channels, and the doped region is disposed below a bottomone of the plurality of channels.
 9. The integrated circuit of claim 8,wherein the gate stack includes a gate dielectric layer and a gateelectrode, the gate dielectric layer is surrounding the each of theplurality of channels, and the gate electrode is surrounding the each ofthe plurality of channels.
 10. A method, comprising: forming a sourceand a drain on a semiconductor substrate, wherein the source and thedrain are doped with a first-type conductivity; forming a channel dopedof a second-type conductivity being opposite to the first-typeconductivity; forming a doped feature of the first-type conductivity,wherein the doped feature is underlying the channel and connects thesource and the drain; and forming a gate stack that includes forming agate dielectric layer and a gate electrode, wherein the source, thedrain, the channel and the gate stack are components of a de-cap devicehaving the source and the drain connected through an interconnectionstructure.
 11. The method of claim 10, wherein the forming a channelincludes forming a plurality of channels between the source and thedrain, wherein the channels are vertically stacked; and the forming gatestack includes forming a gate dielectric layer and a gate electrode bothextended to be around each of the plurality of channels.
 12. The methodof claim 11, wherein the forming a doped feature includes forming thedoped feature below the plurality of channels.
 13. The method of claim10, wherein the forming a doped feature includes forming a patternedmask using a lithography process, wherein the patterned mask includes afirst opening for an anti-punch-through (APT) feature to a field-effecttransistor (FET) of a first-type conductivity and a second opening forthe doped feature of the de-cap device with source and the drain havinga second-type conductivity being opposite to the first-typeconductivity; and performing an ion implantation process through thepatterned mask using a dopant of the second-type conductivity, therebyforming the doped feature and the APT feature.
 14. The method of claim13, further comprising forming a first fin active region on thesemiconductor substrate; and forming a first shallow trench isolation(STI) feature on the semiconductor substrate and surrounding the firstfin active region, wherein a top surface of the first fin active regionis above a top surface of the first STI feature, and the forming asource and a drain includes forming the source and the drain on the finactive region.
 15. The method of claim 14, further comprising: forming asecond fin active region; and forming a second STI feature surroundingthe second fin active region, wherein the second STI feature includes atop surface above the top surface of the first STI feature and below thetop surface of the first fin active region, and wherein the FET isformed on the second fin active region.
 16. An integrated circuit,comprising: a first fin active region and a second fin active region ona semiconductor substrate; a first sallow-trench isolation (STI) featuresurrounding the first fin active region; a second sallow-trenchisolation (STI) feature surrounding the second fin active region, thefirst STI feature includes a top surface above a top surface of thesecond STI feature and below a top surface of the first and second finactive regions; a circuit having a first field-effect transistor (FET)formed on the first fin active region; and a de-cap device formed on thesecond fin active region, wherein the de-cap device includes a secondFET that further includes a source and a drain connected through contactfeatures landing on the source and drain, respectively, and a gate stackinterposed between the source and the drain, wherein the second FET is agate-all-around FET (GAA-FET) including a plurality of channelsvertically stacked on the semiconductor substrate, the gate stack isextended to be around each of the plurality of channels, and each of thesource and the drain extends down to be connected to each of theplurality of channels.
 17. The integrated circuit of claim 16, furthercomprising a doped feature disposed underlying the plurality of channelsand connecting to the source and the drain, wherein the doped feature isdisposed below the plurality of channels.
 18. The integrated circuit ofclaim 16, further comprising a doped feature doped with a dopant of asame type of the source and the drain and contacting to bottom surfacesof the source and drain.
 19. The integrated circuit of claim 18, whereinthe plurality of channels is doped with a dopant opposite to the dopantof the doped feature.
 20. The integrated circuit of claim 18, whereinthe second FET is a p-type FET, the source and the drain are p-typedoped, and the doped feature is p-type doped; the first FET is an n-typeFET that includes multiple channels vertically stacked and ananti-punch-through (APT) feature disposed underlying the multiplechannels; and the APT feature is p-type doped.